Hardfacing of metal surfaces and substrates is a well known technique to minimize or prevent erosion and abrasion of the metal surface or substrate. Hardfacing can be generally defined as applying a layer of hard, abrasion resistant material to a less resistant surface or substrate by plating, welding, spraying or other well known deposition techniques. Hardfacing is frequently used to extend the service life of drill bits and other downhole tools used in the oil and gas industry. Tungsten carbide and its various alloys are some of the more widely used hardfacing materials to protect drill bits and other downhole tools associated with drilling and producing oil and gas wells.
Hardfacing is typically a mixture of a hard, wear-resistant material embedded in a matrix deposit which is preferably fused with the surface of a substrate by forming metallurgical type bonds to ensure uniform adherence of the hardfacing to the substrate. For some applications, wear-resistant material such as an alloy of tungsten carbide and/or cobalt is placed in a steel tube which serves as a welding rod during welding of the hardfacing with the substrate. This technique of applying hardfacing is sometimes referred to as "tube rod welding." Tungsten carbide/cobalt hardfacing applied with tube rods has been highly successful in extending the service life of drill bits and other downhole tools.
Rotary cone drill bits are often used for drilling boreholes for the exploration and production of oil and gas. This type of bit typically employs three rolling cone cutters, also known as rotary cone cutters, rotatably mounted on spindles extending from support arms of the bit. The cutters are mounted on respective spindles that typically extend downwardly and inwardly with respect to the bit axis so that the conical sides of the cutters tend to roll on the bottom of a borehole and contact the formation.
For some applications, milled teeth are formed on the cutters to cut and gouge in those areas that engage the bottom and peripheral wall of the borehole during the drilling operation. The service life of milled teeth may be improved by the addition of tungsten carbide particles to hard metal deposits on selected wear areas of the milled teeth. This operation is sometimes referred to as "hardfacing." U.S. Pat. No. 4,262,761, issued Apr. 21, 1981 discloses the application of hardfacing to milled teeth and is incorporated by reference for all purposes within this application.
For other applications, sockets may be formed in the exterior of the cutters and hard metal inserts placed in the sockets to cut and gouge in those areas that engage the bottom and peripheral wall of the borehole during the drilling operation. The service life of such inserts and cutters may be improved by carburizing the exterior surface of the cutters. U.S. Pat. No. 4,679,640 issued on Jul. 14, 1987 discloses one procedure for carburizing cutters and is incorporated by reference for all purposes within this application.
A wide variety of hardfacing materials have been satisfactorily used on drill bits and other downhole tools. A frequently used hardfacing includes sintered tungsten carbide particles in an alloy steel matrix deposit. Other forms of tungsten carbide particles may include grains of monotungsten carbide, ditungsten carbide and/or macrocrystalline tungsten carbide. Satisfactory binders may include materials such as cobalt, iron, nickel, alloys of iron and other metallic alloys. For some applications loose hardfacing material is generally placed in a hollow tube or welding rod and applied to the substrate using conventional welding techniques. As a result of the welding process, a matrix deposit including both steel alloy melted from the substrate surface and steel alloy provided by the welding rod or hollow tube is formed with the hardfacing. Various alloys of cobalt, nickel and/or steel may be used as part of the binder for the matrix deposit. Other heavy metal carbides and nitrides, in addition to tungsten carbide, have been used to form hardfacing.
Both natural and synthetic diamonds have been used in downhole drill bits to provide cutting surfaces and wear-resistant surfaces. U.S. Pat. No. 4,140,189 teaches the use of diamond inserts protruding from the shirttail surface of a roller cone bit. Polycrystalline diamond (PCD) gauge inserts are frequently used on a wide variety of drill bits to prevent erosion and wear associated with harsh downhole drilling conditions. U.S. Pat. No. 4,140,189 is incorporated by reference for all purposes within this application.